From 3d5bd95558a0a6beb48531eea60994c694208b4a Mon Sep 17 00:00:00 2001
From: Veera <sveera.2001@gmail.com>
Date: Mon, 29 Jul 2024 21:47:42 -0400
Subject: [PATCH] Fix ICE Caused by Incorrectly Delaying E0107

---
 compiler/rustc_hir/src/hir.rs                 |  5 +++
 .../src/hir_ty_lowering/generics.rs           | 41 ++++++++++++-------
 2 files changed, 32 insertions(+), 14 deletions(-)

diff --git a/compiler/rustc_hir/src/hir.rs b/compiler/rustc_hir/src/hir.rs
index 3b9aea087910a..b137a279de43d 100644
--- a/compiler/rustc_hir/src/hir.rs
+++ b/compiler/rustc_hir/src/hir.rs
@@ -3689,6 +3689,11 @@ impl<'hir> OwnerNode<'hir> {
         }
     }
 
+    /// Check if node is an impl block.
+    pub fn is_impl_block(&self) -> bool {
+        matches!(self, OwnerNode::Item(Item { kind: ItemKind::Impl(_), .. }))
+    }
+
     expect_methods_self! {
         expect_item,         &'hir Item<'hir>,        OwnerNode::Item(n),        n;
         expect_foreign_item, &'hir ForeignItem<'hir>, OwnerNode::ForeignItem(n), n;
diff --git a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
index f18224c39ae49..034a4918b505f 100644
--- a/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
+++ b/compiler/rustc_hir_analysis/src/hir_ty_lowering/generics.rs
@@ -552,21 +552,34 @@ pub(crate) fn check_generic_arg_count(
                 synth_provided,
             }
         } else {
-            let num_missing_args = expected_max - provided;
+            // Check if associated type bounds are incorrectly written in impl block header like:
+            // ```
+            // trait Foo<T> {}
+            // impl Foo<T: Default> for u8 {}
+            // ```
+            let parent_is_impl_block = cx
+                .tcx()
+                .hir()
+                .parent_owner_iter(seg.hir_id)
+                .next()
+                .is_some_and(|(_, owner_node)| owner_node.is_impl_block());
+            if parent_is_impl_block {
+                let constraint_names: Vec<_> =
+                    gen_args.constraints.iter().map(|b| b.ident.name).collect();
+                let param_names: Vec<_> = gen_params
+                    .own_params
+                    .iter()
+                    .filter(|param| !has_self || param.index != 0) // Assumes `Self` will always be the first parameter
+                    .map(|param| param.name)
+                    .collect();
+                if constraint_names == param_names {
+                    // We set this to true and delay emitting `WrongNumberOfGenericArgs`
+                    // to provide a succinct error for cases like issue #113073
+                    all_params_are_binded = true;
+                };
+            }
 
-            let constraint_names: Vec<_> =
-                gen_args.constraints.iter().map(|b| b.ident.name).collect();
-            let param_names: Vec<_> = gen_params
-                .own_params
-                .iter()
-                .filter(|param| !has_self || param.index != 0) // Assumes `Self` will always be the first parameter
-                .map(|param| param.name)
-                .collect();
-            if constraint_names == param_names {
-                // We set this to true and delay emitting `WrongNumberOfGenericArgs`
-                // to provide a succinct error for cases like issue #113073
-                all_params_are_binded = true;
-            };
+            let num_missing_args = expected_max - provided;
 
             GenericArgsInfo::MissingTypesOrConsts {
                 num_missing_args,